Chlorophyll patterns and the underlying dynamics were studied near eddies in the northern South China Sea based on the observations of satellite data and ship measurements as well as a high-resolution physical and biological model in 2018 summer. It was found that eddies had shallower depth, thicker thickness and higher chlorophyll in the subsurface chlorophyll maximum (SCM) layers in the eddy edge, compared with those in the eddy interior. An eddy pair were taken as an example for further study. The anticyclonic eddy had deeper depth, thicker thickness and lower chlorophyll in the SCM layer than the cyclonic eddy. Further, model results implied that nutrient supply and chlorophyll pattern in the cyclonic eddy were mainly affected by eddy advection, next by submesoscale processes, thirdly by Eddy pumping, and lastly by Eddy-wind interactions. In the eddy-pair transition region, eddy advection and eddy pumping turned weaker, while submesoscale processes and the traditional Wind-Eddy interactions were intensified. In the anticyclonic eddy, eddy advection and submesoscale processes was gradually reduced, and was close to the traditional eddy-wind interactions, all of which were stronger than eddy pumping. Thus, eddy advection, eddy pumping, the traditional Eddy-Wind interactions and submesoscale processes were important for nutrient supply and chlorophyll patterns near eddies. It is worth noting that the contributions of each process may change in different stage of eddy lifecycle as well as in different season when surface wind and circulations in the South China Sea evolved.

Eddy; chlorophyll; submeoscale processes; subsurface chlorophyll maximum (SCM); physical and biological dynamics